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Discussion papers
https://doi.org/10.5194/acp-2019-270
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-270
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 12 Apr 2019

Research article | 12 Apr 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).

Size-resolved Composition and Morphology of Particulate Matter During the Southwest Monsoon in Metro Manila, Philippines

Melliza Templonuevo Cruz1,2, Paola Angela Bañaga1,3, Grace Betito3, Rachel A. Braun4, Connor Stahl4, Mojtaba Azadi Aghdam1, Maria Obiminda Cambaliza1,3, Hossein Dadashazar4, Miguel Ricardo Hilario3, Genevieve Rose Lorenzo1, Lin Ma4, Alexander B. MacDonald4, Preciosa Corazon Pabroa5, John Robin Yee5, James Bernard Simpas1,3, and Armin Sorooshian4,6 Melliza Templonuevo Cruz et al.
  • 1Manila Observatory, Quezon City 1101, Philippines
  • 2Institute of Environmental Science and Meteorology, University of the Philippines, Diliman, Quezon City 1101, Philippines
  • 3Department of Physics, School of Science and Engineering, Ateneo de Manila University, Quezon City 1101, Philippines
  • 4Department of Chemical and Environmental Engineering, University of Arizona, Tucson, AZ, USA
  • 5Philippine Nuclear Research Institute, Commonwealth Avenue, Diliman, Quezon City 1101, Philippines
  • 6Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ, USA

Abstract. This paper presents novel results from size-resolved particulate matter (PM) mass, composition, and morphology measurements conducted during the 2018 Southwest Monsoon (SWM) season in Metro Manila, Philippines. Micro-Orifice Uniform Deposit Impactors (MOUDIs) were used to collect PM sample sets that were analyzed for mass, morphology, black carbon (BC), and composition of the water-soluble fraction. The bulk of the PM mass was between 0.18–1.0 µm with a dominant mode between 0.32–0.56 µm. Similarly, most of the black carbon (BC) mass was found between 0.10–1.0 µm (the so-called Greenfield gap), peaking between 0.18–0.32 µm, where wet scavenging by rain is inefficient. In the range of 0.10–0.18 µm, BC constituted 78.1 % of the measured mass. Comparable contributions of BC (26.9 %) and the water-soluble fraction (31.3 %) to total PM were observed and most of the unresolved mass, which in total amounted to 41.8 %, was for diameters exceeding 0.32 µm. The water-soluble ions and elements exhibited an average combined concentration of 8.53 µg m−3, with SO42−, NH4+, NO3, Na+, and Cl as the major contributors. Positive Matrix Factorization (PMF) was applied to identify the possible aerosol sources and estimate their contribution to the water-soluble fraction of collected PM. The factor with the highest contribution was attributed to Aged/Transported aerosol (48.0 %) while Sea Salt (22.5 %) and “Combustion” emissions (18.7 %) had comparable contributions. Vehicular/Resuspended Dust (5.6 %) as well as Waste Processing emissions (5.1 %) were also identified. Microscopy analysis highlighted the ubiquity of non-spherical particles regardless of size, which is significant when considering calculations of parameters such as single scattering albedo, asymmetry parameter, and extinction efficiency.

Results of this work have implications for aerosol impacts on public health, visibility, and regional climate as each of these depend on physicochemical properties of particles as a function of size. The significant influence from Aged/Transported aerosol to Metro Manila during the SWM season indicates that local sources in this megacity do not fully govern this coastal area's aerosol properties and that PM in Southeast Asia can travel long distances regardless of the significant precipitation and potential wet scavenging that could occur. That the majority of the regional aerosol mass burden is accounted for by BC and other insoluble components has important downstream effects on the aerosol hygroscopic properties, which depend on composition. The results are relevant for understanding the impacts of monsoonal features on size-resolved aerosol properties, notably aqueous processing and wet scavenging. Finally, the results of this work provide contextual data for future sampling campaigns in Southeast Asia such as the airborne component of the Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex) planned for the SWM season in 2019. Aerosol characterization via remote-sensing is notoriously difficult in Southeast Asia, which elevates the importance of datasets such as the one presented here.

Melliza Templonuevo Cruz et al.
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Short summary
This study is the first to report size-resolved PM mass and composition in Metro Manila, Philippines. The results, which focus on the southwest monsoon season (SWM), are important with regard to understanding the competition between local sources and long range transport; characterizing the properties of aerosol impacted by both aqueous processing and wet scavenging; and providing contextual data for comparison with other monsoonal regions and coastal megacities.
This study is the first to report size-resolved PM mass and composition in Metro Manila,...
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